The present invention disclosed herein relates to a wireless signal receiver for wireless communication, and more particularly, to a multi-band receiver for receiving and directly down-converting a plurality of signals transmitted at different bands.
Recently, terminals for wireless communication systems have become more compact and have been improved to satisfy new requirements of various standards of wireless communication. In particular, such terminals are required to support both a multi-band and a multi-mode for improving flexibility, adaptability and cognitivity. Moreover, next-generation wireless communication standards will provide dynamic spectrum allocation and sharing functions to improve the spectrum efficiency and the quality of service (QoS). Furthermore, non-contiguous frequency bands may be allocated to improve the efficiency of use of a spectrum. Such requirements need a technology for receiving signals transmitted at two or more different frequency bands using a single receiver.
Currently, it is required to simultaneously support two or more different communication standards in a single wireless receiver, or, in the case of a communication system such as a cognitive radio communication system, it is required to scan signals at an arbitrary frequency band, while receiving signals of another arbitrary frequency band. However, a typical receiver should be provided with separate receiver circuits or chips for respective modes and respective frequency bands or channels. Therefore, the circuit structure of the receiver is complicated and the unit price of the receiver is high. Therefore, a novel receiver for supporting a multi-band and a multi-mode using a single receiver circuit is required.
A band-pass sampling technology is considered as one of the best alternatives for satisfying such requirements. According to the band-pass sampling technology, sampling is performed at a sampling rate that is at least two times higher than a signal bandwidth so that an RF band signal is directly frequency-converted into a baseband signal. A typical band-pass sampling receiver applies two sampling clocks having relative time delays to two analog-to-digital converts (ADCs) respectively to perform sampling, and then removes an aliasing effect through signal processing. However, since such a band-pass sampling receiver needs two ADCs, the complexity of hardware increases. Furthermore, since a delay time difference between two paths is induced by using analog devices, the performance of hardware may be degraded due to an error of the delay time difference between the paths and irregular signal magnitude.